The problem of optimizing a saturated steam thermodynamic cycle in a plant for generating electricity from nuclear energy has been tackled by means of a number of methods and devices, notably by using a drying and/or superheating stage in a saturated steam thermodynamic cycle in a plant of this kind between a high-pressure turbine module and a lower-pressure turbine module, and by installing an associated device.
Methods and devices of this kind make use of live steam; that is to say, the steam from the boiler is used to superheat the steam between the high pressure and the lower pressure parts.
Thus, in known configurations, of which a known variant is shown in FIG. 1, a dryer 70 and a superheater 80 are placed between a high-pressure module 30 and a medium-pressure module 40, and are adapted to dry and superheat the steam output by the high-pressure module, this steam being generated by a steam generator 140 upstream of said high-pressure module, said steam generator 140 being supplied by a nuclear energy source 140′. Additionally, for the purpose of superheating, the superheater 80 is supplied with live steam through a pipe 270 connected to the outlet of the steam generator 140.
The drawbacks of these methods and associated devices include, notably, the requirement for a high degree of superheating to enable the steam to flow through the lower-pressure turbine without rapidly generating water droplets which would have negative effects on efficiency and which would also tend to degrade the turbine. Furthermore, the use of live steam for superheating has little effect on the efficiency of the nuclear cycle, because this energy is recovered in the form of heat alone, and is not converted into electricity. This is because, whereas the steam in a fossil fuel powered electricity generating plant is reheated directly by the boiler, thus increasing the mean temperature of the heat exchange and improving the efficiency of the cycle, superheating by live steam in a nuclear-powered plant can only degrade the thermodynamic cycle. However, superheating can reduce the losses due to the moisture content in the final expansion stages. This positive effect is greater than the negative effect due to the degradation of the cycle in correctly optimized plants. Furthermore, this analysis confirms the greater importance of drying, which contributes to a reduction of the losses due to moisture content in the downstream expansion stages.